A mother and her 12-month-old son, who are still unaccounted for after an explosion at Rozelle have been identified as Bianka O'Brien and her child, Jude.

If it had exploded upwards and not outwards I don't think I would be talking to you ... I'm wearing one sock and my clothes, that's all I've got

It is believed Ms O'Brien, 31, is the sister of James Keremelevski, who owns a mobile phone shop next to the convenience store that was obliterated by an explosion on Darling Street just after 4am on Thursday.

Cars were destroyed by the blast. Photo: Peter Rae

Police said a 30-year-old man who has also not been accounted for was not a relation of Ms O'Brien and her baby boy.

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In the past few months, a doting Ms O'Brien shared beautiful portraits of her son with her friends online.

She also posted many loving pictures with her husband, John.

Firefighters outside the Rozelle shop that was destroyed in the explosion. Photo: Peter Rae

In recent months the close couple had taken their son on his first ferry ride and spoke about how well behaved he was.

"John was a good baby, so I would say Jude is just like him," she posted on Facebook.

Inspector Clive Ainley, the commander of the Leichhardt local area command, said he could not comment on reports that a fourth person was also missing.

Firefighters battled to contain the blaze. Photo: Peter Rae

"The information we have right now is that three people are unaccounted for," he said.

Store engulfed in flames

Emergency services arrived to find the store, on Darling Street in Rozelle, engulfed in flames just after 4am on Thursday.

Firefighters had not been able to search the building thoroughly due to the further risk of collapse as it was structurally unsound and it might be hours before they could enter, a Fire and Rescue NSW spokesman said.

Search and rescue teams, consisting of highly trained emergency service workers, are assessing how they will get into the building to search for potential victims.

Firefighters had to withdraw from the building gradually throughout Thursday morning due to major safety concerns, Superintendent Paul Johnstone, from Fire and Rescue NSW, said.

Blast: the shop went up in flames. Photo: Anthony Carroll

"Throughout the morning, as the building has continued to collapse, we've had to withdraw troops, and now the latest firefighting ... had to be done through our cherry picker-type fire engines," he said.

"We haven't been able to get right throughout the building now due to the collapse and how dangerous the scene is," he said.

Superintendent Johnstone said he was unsure how many apartments were located above the store, due to the scale of the destruction.

"I believe there was a residence upstairs. Two of the people that did escape from the building jumped form the first floor, so I'd say the residences were upstairs and the shop downstairs, that's what seems to be the layout.

"But it's impossible to tell from what we've got there at the moment," he said.

"As horrific as it is down there, we are still holding out hope there may be some survivors," he said.

The school says pedestrian access to the school is possible via Darling Street and Wellington Street.

Car access in the area is very limited. Parents are advised to park on the Lilyfield side of Victoria Road, or other nearby street, and walk to the school.

Road closures are expected to be in place for an extended period.

Bianka O'Brien with her child Jude. Photo: Facebook

Owner trapped under rubble

Rozelle residents said they were woken by an "almighty bang", which some mistook for a lightning strike, just after 4am.

The blast was so loud it could be heard in the surrounding suburbs of Balmain, Drummoyne and Camperdown. It also blew out the windows of restaurants and stores on the opposite side of Darling Street, and of homes in surrounding streets.

The building was engulfed in flames moments later, its owner trapped under a commercial fridge after the roof collapsed.

Fire and Rescue NSW said the store owner was trapped under so much rubble that only his hands were visible when crews arrived.

Two residents upstairs had to jump from their balcony into Darling Street below to make it out alive.

All three men were taken to Royal Prince Alfred Hospital, police said.

The shop owner had serious head and leg injuries, while the two residents suffered minor injuries from exploding glass.

Investigators believe the explosion is suspicious, but have not commented on witness reports that a car was seen speeding away from the convenience store moments before the blast.

It is understood council workers were collecting rubbish on Darling Street and saw the car do a hasty U-turn just before the explosion.

Inspector Coffey said fire investigators were yet to search the convenience store thoroughly to determine the cause of the fire. He would not comment on the report of the speeding car.

"We're still in the process of trying to gather witnesses and information about exactly what occurred in the moments before the fire started," he said.

Inspector Ainley said: "We've received a lot of information, we're following all those leads. There was a car that was reported driving away at that time. I don't know what part that car plays in this investigation at the moment."

Escaped with just phone and clothes

Anthony Carroll, who lived with his father in a unit above the convenience store, said he was fast asleep when he was woken by the explosion.

Mr Carroll said he turned on his bedroom light and saw smoke coming in under the door.

"Within 30 seconds, my room was full of smoke," he said.

"I just grabbed what I've got on and got out of there.

"There were people screaming and yelling and people trapped in the place next door so it was pandemonium.

"No one knew what was going on."

He escaped with just his phone and the clothes he was wearing.

"If it had exploded upwards and not outwards I don't think I would be talking to you," he said.

"There was an explosion first and then the fire.

"One of the other guys who lives upstairs got out; he was covered in blood.

"The store owner was downstairs and the roof collapsed on him, and the other bloke upstairs was trapped but he eventually managed to get out," he said.

"It was just a massive explosion. An almighty bang. I turned the light on, there was smoke in the room, I threw my tracksuit pants on, grabbed my phone.

"I'm wearing one sock and my clothes, that's all I've got."

He said that, in the moments after the explosion, one of the men was screaming that his housemate was still trapped inside.

Mr Carroll said firefighters told him he would not be able to get back into his place for at least a day, but he expects everything has been destroyed.

"I've been a bit emotional about it," he said.

"I'm lucky, it made me appreciate how lucky we are to live in a country like this because there are people that wake up to this every minute of the day.

"God knows what it was."

Witness reports

Resident Jessica Davis who lives diagonally opposite the site of the explosion said she and her boyfriend woke up suddenly when they heard a big "bang" about 4am. They watched the front of the shop collapse from the force of the blast.

"The building just fell down in front of all the firefighters," she said.

"It was really frightening. All the neighbours came out and people were still in their pyjamas."

Ms Davis said that, while she knew many of the shop owners along the street, the convenience store had recently changed hands.

Rozelle resident Shan Handran-Smithlives about 50 metres from the convenience store, and was a regular customer there.

She said she was woken about 4am to what she thought was an explosion or possibly lightning striking a tree. It was a "really powerful noise".

"I was in a bit of shock, because the noise was so loud, and I looked out the window and there was smoke," Ms Handran-Smith said.

"My neighbour's window had been broken. The noise had smashed the windows of some of the local houses.

"So I went outside and [the convenience store] is only about maybe 50 metres from my house.

"I got to the top of the street and only the fire brigade had got there. There was a car on fire, a shop front on fire, the smell of burning rubber was through the air. I asked another onlooker and they said a tyre had exploded."

Ms Handran-Smith said about 50 people had emerged from their homes, some in their pyjamas, to see what had happened.

"There was debris everywhere. Shards of glass had spread hundreds of metres down the street, far from where the actual explosion took place," she said.

"There's a young family who live in the units above the shops directly across the road from where the fire was. They were holding their baby and looking really, really worried. Everyone was just really spooked."

Ms Handran-Smith said she often went into the family-run convenience store to buy her bus ticket.

"As soon as I realised where the fire was, I felt a bit ill thinking about what had happened. I hope they're all right," she said.

Long-term Rozelle resident Vicky Apostolou said she had never heard a noise like the one that jolted her out of bed early on Thursday morning.

"I heard 'boom'," Mrs Apostolou said.

"I get up because I'm scared. This is the first time in my life I heard this noise," she said.

Mrs Apostolou lives 100 metres from where the explosion demolished the convenience store but said she had not gone outside to survey the damage.

"I was scared to go out because my son and husband are overseas. I've not gone outside to look," she said.

Tania Wursig lives a few doors down from the blast site and said many residents were worried about those who were missing.

"Everyone knows each other around here. I can't describe it, it's a very eerie feeling and the possibility that someone might be dead is weird," Ms Wursig said.

"If they were in that building ... the building is not there any more," she said.

Ms Wursig said she did not hear the explosion but was shocked when she saw that a building had been completely demolished.

"I live above a shop as well, above a bakery and I am thinking 'How would I get out?' It's very concerning."